Solvent extraction of an infusible material typically involves the removal of one or more of the extractable constituents of an infusible material, by contact with a solvent, to form an extract. In many common extractions, a suitable solvent material may be mixed with an infusible material, resulting in a mixture of an extract and the infusible material after extraction has taken place. An exemplary common type of extraction is the extraction of constituents from infusible plant-based materials using water, and particularly hot water, as a solvent, to form a mixture of a substantially aqueous extract and the infusible plant-based material after extraction has taken place.
A number of input parameters affecting the process of extraction may be associated with the characteristics of the infusible material itself, independent from the solvent extraction apparatus. Three exemplary known infusible material characteristics in particular include:                the mass of infusible material;        the time between crushing or grinding (if required) of the infusible material and the extraction process;        the particle size and particle size distribution of the infusible material.        
A further number of input parameters known to affect the process of extraction may typically be controlled by the solvent extraction apparatus and method of performing the extraction. Such exemplary extraction parameters related to the extraction apparatus and method of use include:                the volume of solvent relative to the volume or mass of infusible material;        the extraction time (contact time of the solvent with the infusible material);        the temperature of the mixture of infusible material and extract (note that the initial solvent temperature may be set externally from the solvent extraction apparatus, such as in the example of externally heated water). The temperature of the mixture may also vary over time, due to cooling for example.        the effective aperture size of the filtering means used to separate the extract from the infusible material, after the extraction is complete.        
The final properties of the extract produced by a solvent extraction process are typically affected and controlled by the above-described infusible material and extraction apparatus and method characteristics. Exemplary such final properties of the extract resulting from the solvent extraction process include:                the final temperature of the extract;        the soluble constituents of the infusible material contained in the extract;        the insoluble constituents of the infusible material contained in the extract (e.g. fine particles of the infusible material and/or insoluble oils extracted from the infusible material that pass through the filtering means);        the volume of extract produced.        
For many common solvent extractions, particularly exemplary solvent extractions of plant materials using hot water to produce a beverage such as coffee or tea, for example, the preferred characteristics for the extraction process may be similar. For example, in some common exemplary extractions, smaller particles of the infusible material may be preferred over larger particles, since with larger particles, the outer surface of the particles may be undesirably over-extracted by the solvent during the extraction, while the inner core of the larger particles remains undesirably under-extracted. In such a case, the use of smaller infusible material particles may desirably contribute to more consistent extraction of the infusible material particles. Further, the extraction process may also proceed more quickly using smaller particles of infusible material, and therefore desirably take less time to complete. Such desirable faster extraction may also facilitate a more consistent temperature throughout the extraction, particularly in cases where a non-heated solvent extraction apparatus is used, wherein hot solvent, such as hot water for example, is placed in the extraction apparatus at an initial temperature, and the temperature of the extract and infusible material mixture decreases as the extraction process proceeds. Accordingly, there may typically exist a preferred extraction time period for a given infusible material particle size, wherein the preferred extraction time is shorter for relatively smaller particle sizes.
An additional desirable benefit of using smaller particles of infusible material for an extraction process may be realized in extractions where the infusible material and the extract separate due to density (i.e. wherein the infusible material generally floats or sinks in the extract). In such cases of unequal infusible material and extract densities such as in the exemplary case of extractions to produce coffee where the infusible material typically floats in the extract, if larger infusible material particles are used, the resulting slower extraction process may undesirably over-extract the bottom layers of the infusible material in contact with the extract, and undesirably under-extract the top layers of the infusible material which may be floating substantially above the extract. In such cases, the use of smaller infusible material particles which may complete extraction more quickly may desirably reduce the occurrence of such under and over-extraction.
In some common exemplary extractions, the above-described relatively faster extraction resulting from using smaller infusible material particles may also desirably reduce the extraction of some undesirable constituents of infusible material. For example, in the case of coffee extractions, faster extraction may desirably reduce the amount of caffeine extracted from the infusible material. Relatively high levels of caffeine may be undesirable due to its bitter flavour and stimulant properties. Additionally, relatively faster extraction may reduce variation in temperature of the extract and infusible material mixture during extraction using some types of extraction apparatus, as described above. Such reduced temperature variation may reduce extraction of sour constituents of coffee by lower than ideal temperature extraction, or reduce extraction of bitter constituents of coffee by higher than ideal temperature extraction, for example.
For reasons such as those detailed above, the use of relatively fine infusible material particles may be desirable for conducting extractions to produce a desirable extract product. However, some exemplary commonly known extraction apparati, such as a traditional french press coffee and/or tea making apparatus, for example, may be limited in the lower bounds of infusible material particle size that are practical for use in the apparatus. In some common extraction apparati like an exemplary french coffee press, and variations thereon, a piston or filter component is used to separate infusible material from the extract upon completion of extraction. Such separation may be achieved by physically filtering the extract to flow through a layer of retained infusible material accumulated on the surface of the piston or filter component and then through a filtering means in the piston or filter component as the piston or filter is pushed through the mixture of extract and infusible material from one end of the extraction apparatus to the other. In other similar known extraction apparati, a piston or filter component may be powered mechanically or pneumatically, for example to physically move the component and filter the extract.
Although smaller infusible material particle size may be desirable as explained above, commonly known extraction apparati such as a french coffee press as described above typically cannot function acceptably with infusible particle sizes below a certain size, as such smaller particles may typically unacceptably clog the filtering means, or pass through or around the filtering means and into the extract. Common unacceptable outcomes of filter medium clogging in known extraction apparati may include:                making it difficult or impossible to push the extract through the clogged filter and accumulated infusible material, which may result in the application of excessive pressure to a piston or filter component which in an extreme case could lead to breakage of the apparatus or potential frustration and/or harm to a user;        passage of unacceptable amounts of small infusible material particles around the piston or filter component or seals associated therewith, which then become undesirably entrained in the extract, which may result in an unwanted muddy or gritty texture to the extract; and        passage of unacceptable concentrations of small infusible material particles (fines) through the filter and into the extract. The solvent in the extract may then continue the extraction process on such passed infusible material and extract undesirable constituents of the infusible material degrading the quality of the extract or even render the extract unpalatable in the case of a beverage extract.        
Due to the undesirable results of using smaller infusible material particles in some common extraction apparati as described above, many such common extraction apparati according to the prior art (such as french coffee and/or tea press apparati for example) have effectively required the use of larger particle sizes for infusible materials in order to allow separation of the resulting extract and infusible material by use of a piston and filter component. Such required larger infusible material particles typically result in a slower progress of the extraction process, and therefore typically necessitates a relatively longer extraction time. Longer extraction times associated with use of some common extraction apparati may undesirably reduce the quality of the resultant extract by such exemplary factors as:                over-extraction of the outer surfaces of the infusible material particles, while leaving the inner core of such particles under-extracted;        time waste and delay due to longer extraction times required;        potential increase in extraction of certain extraction duration-sensitive undesirable constituents, such as caffeine, or increase in undesirable characteristics of the extract due to either over or under-extraction of the infusible material; and        potential increase in variation of the temperature of the extraction due to cooling of the extract/infusible material mixture in unheated extraction apparati, which may undesirably change the amount of certain temperature-sensitive extractable constituents which may be extracted from the infusible material.        